---
id: a9f15484-b4d0-40cc-bd64-0c21a6d3b0ba
---

# MySQL too many connections incident
---

This incident type occurs when the number of concurrent connections to a MySQL database server exceeds the configured limit of 80%. This can lead to performance degradation or even database server crashes, making the application or system that relies on the database server unavailable for the end-users. This type of incident typically requires immediate attention and resolution to restore normal operation of the affected service.

### Parameters
```shell
# Environment Variables

export PASSWORD="PLACEHOLDER"

export USERNAME="PLACEHOLDER"

export MAX_CONNECTIONS="PLACEHOLDER"

export PATH_TO_MYSQL_CONF="PLACEHOLDER"

```

## Debug

### Check MySQL server status
```shell
systemctl status mysql
```

### Check the current number of connections to the MySQL server
```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW STATUS WHERE `variable_name` = 'Threads_connected';"
```

### Check the maximum number of connections allowed by the MySQL server
```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW VARIABLES LIKE 'max_connections';"
```

### Check the current MySQL process list to see the active connections
```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW PROCESSLIST;"
```

### Check the system load average and CPU usage
```shell
top
```

### Check the available memory and swap usage
```shell
free -m
```

### Check the disk space usage
```shell
df -h
```

### Check the MySQL slow query log
```shell
tail -f /var/log/mysql/mysql-slow.log
```

### Check the MySQL error log
```shell
tail -f /var/log/mysql/error.log
```

## Repair

### Define variables
```shell
MYSQL_CONF=${PATH_TO_MYSQL_CONF}  # Replace with the path to your MySQL configuration file

MAX_CONNECTIONS=${MAX_CONNECTIONS}  # Replace with the desired maximum number of connections
```
### Check if the MySQL configuration file exists
```shell
if [ ! -f $MYSQL_CONF ]; then

  echo "Error: MySQL configuration file not found: $MYSQL_CONF"

  exit 1

fi
```
### Replace the max_connections parameter in the MySQL configuration file
```shell
sed -i "s/^max_connections.*/max_connections = $MAX_CONNECTIONS/" $MYSQL_CONF
```

### Restart the MySQL service to apply the changes
```shell
systemctl restart mysql.service  # Replace with the command to restart your MySQL service
```

### Identify and terminate idle connections to the database server to free up resources for other connections.
```shell
#!/bin/bash

# Get the list of idle MySQL connections

IDLE_CONNECTIONS=$(mysql -u $MYSQL_USER -p$MYSQL_PASSWORD -e "SHOW PROCESSLIST" | awk '{if ($6 == "Sleep") print $1}')

# Terminate idle connections

for connection in $IDLE_CONNECTIONS

do

    mysql -u $MYSQL_USER -p$MYSQL_PASSWORD -e "KILL $connection"

done

echo "Idle MySQL connections terminated."

```

This incident type occurs when the number of concurrent connections to a MySQL database server exceeds the configured limit of 80%. This can lead to performance degradation or even database server crashes, making the application or system that relies on the database server unavailable for the end-users. This type of incident typically requires immediate attention and resolution to restore normal operation of the affected service.


This incident type is related to the Tomcat server, which is a popular open-source Java application server. It occurs when the available threads in the connection pool are running low, which means that there are not enough resources to serve incoming requests. This can cause delays or even failures in the application's performance, impacting the end-user experience. It is important to monitor and address this issue promptly to ensure that the application runs smoothly and efficiently.


Tomcat Low Available Threads in Connection Pool

This incident type refers to a situation where the Tomcat server's JDBC connection pool usage surpasses its configured limits. This can lead to a shortage of available connections for incoming requests, resulting in slow response times or even server crashes. It is important to monitor and manage the JDBC connection pool usage to prevent such incidents from occurring.


Tomcat High JDBC Connection Pool Usage Incident.

Tomcat Connection Pool Exhaustion Incident occurs when the maximum number of connections that a Tomcat server can handle has been reached. This can happen due to an increase in traffic or a sudden surge in user activity. When the connection pool is exhausted, new requests cannot be handled, and the application may become unavailable. This type of incident requires immediate attention to ensure that the application is restored to its normal functioning state.


Tomcat Connection Pool Exhaustion Incident

This incident type refers to a situation where Redis, a popular in-memory data structure store, has rejected connections. This could happen due to various reasons such as server overload, network issues, or misconfiguration. When this occurs, it can cause disruptions in the performance of applications that rely on Redis for data storage or caching. Thus, it requires immediate attention and resolution to minimize the impact on the applications and users.


Redis Rejected Connections Incident

This incident type occurs when the maximum number of connections allowed to a Postgres database has been reached. This prevents new connections from being established and can result in errors or downtime. It is important to monitor connection usage and adjust the maximum connection limit as needed to prevent this issue from occurring.


Postgres Connection Limit Reached

```shell
# Environment Variables

export PASSWORD="PLACEHOLDER"

export USERNAME="PLACEHOLDER"

export MAX_CONNECTIONS="PLACEHOLDER"

export PATH_TO_MYSQL_CONF="PLACEHOLDER"

```


### Check MySQL server status

```shell
systemctl status mysql
```

### Check the current number of connections to the MySQL server

```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW STATUS WHERE `variable_name` = 'Threads_connected';"
```

### Check the maximum number of connections allowed by the MySQL server

```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW VARIABLES LIKE 'max_connections';"
```

### Check the current MySQL process list to see the active connections

```shell
mysql -u ${USERNAME} -p${PASSWORD} -e "SHOW PROCESSLIST;"
```

### Check the system load average and CPU usage

```shell
top
```

### Check the available memory and swap usage

```shell
free -m
```

### Check the disk space usage

```shell
df -h
```

### Check the MySQL slow query log

```shell
tail -f /var/log/mysql/mysql-slow.log
```

### Check the MySQL error log

```shell
tail -f /var/log/mysql/error.log
```


### Define variables

```shell
MYSQL_CONF=${PATH_TO_MYSQL_CONF}  # Replace with the path to your MySQL configuration file

MAX_CONNECTIONS=${MAX_CONNECTIONS}  # Replace with the desired maximum number of connections
```

### Check if the MySQL configuration file exists

```shell
if [ ! -f $MYSQL_CONF ]; then

  echo "Error: MySQL configuration file not found: $MYSQL_CONF"

  exit 1

fi
```

### Replace the max\_connections parameter in the MySQL configuration file

```shell
sed -i "s/^max_connections.*/max_connections = $MAX_CONNECTIONS/" $MYSQL_CONF
```

### Restart the MySQL service to apply the changes

```shell
systemctl restart mysql.service  # Replace with the command to restart your MySQL service
```

### Identify and terminate idle connections to the database server to free up resources for other connections.

```shell
#!/bin/bash

# Get the list of idle MySQL connections

IDLE_CONNECTIONS=$(mysql -u $MYSQL_USER -p$MYSQL_PASSWORD -e "SHOW PROCESSLIST" | awk '{if ($6 == "Sleep") print $1}')

# Terminate idle connections

for connection in $IDLE_CONNECTIONS

do

    mysql -u $MYSQL_USER -p$MYSQL_PASSWORD -e "KILL $connection"

done

echo "Idle MySQL connections terminated."

```


MySQL too many connections incident

Overview

Parameters

Debug

Check MySQL server status

Check the current number of connections to the MySQL server

Check the maximum number of connections allowed by the MySQL server

Check the current MySQL process list to see the active connections

Check the system load average and CPU usage

Check the available memory and swap usage

Check the disk space usage

Check the MySQL slow query log

Check the MySQL error log

Repair

Define variables

Check if the MySQL configuration file exists

Replace the max_connections parameter in the MySQL configuration file

Restart the MySQL service to apply the changes

Identify and terminate idle connections to the database server to free up resources for other connections.

Learn more

Related Runbooks

Tomcat Low Available Threads in Connection Pool

Tomcat High JDBC Connection Pool Usage Incident.

Tomcat Connection Pool Exhaustion Incident

Redis Rejected Connections Incident

Support